To pump aggressive liquids, for example, or water of the highest purity, a complete separation between the drive motor and the pump is required. For such applications, it is known to use a canned motor or gap tube motor which has a tube arranged in the gap between the stator and the rotor. It is also known to suspend the rotor in the gap tube hydrostatically or by means of a sliding bearing. Canned motors have the advantage that the electrical drive side can be hermetically separated by the gap tube or can from the rotating parts and the forwarded medium. Depending on the design of the bearing, the can may be operated for both wet running and dry running. In designing a canned motor it is always important to ensure that the gap tube is sufficiently stable so that the fluid pressure acting on the gap tube does not deform it.
DE 198 45 864 A1 reveals a canned motor having a can that carries the stator windings, the windings resting against the cylindrical outside surface of the can. The can has elements extending outwards around which or within which the windings are wound to create a simply designed canned motor.
EP 1 024 584 A2 relates to a canned motor for a canned centrifugal pump in which two bearings are disposed in the can to journal the shaft. The object of this document is to create a simply designed, easily handled and less expensively fabricated can.
EP 0 846 365 B1 reveals a canned motor having a rotor and a stator as well as a gap tube arranged between the rotor and the stator and at least two bearing apparatuses with at least one of the bearing apparatuses being formed as a bearing and drive apparatus and comprising both an electromagnetic motor drive apparatus and a magnetic bearing apparatus in order to both drive the rotor and to journal it using this bearing and drive apparatus. A sensor to measure the position of the rotor is spatially allocated to the stator in order to measure and regulate the position of the rotor in a radial and axial direction. The rotor position is regulated by means of an active magnetic bearing so that the rotor can rotate freely. The sensor is not capable of or designed to measure the angular position, rotational speed or rotational direction of the rotor.
EP 0 758 154 B1 relates to a canned motor comprising a rotor and a stator and a stator can which is inserted between the rotor and the stator and encloses the rotor. The stator is housed in a stator chamber which is filled with a filler to counteract the expansion of the stator can due to the prevailing fluid pressure in the can. The filler material can be an elastic material or a polymeric material, in particular.
EP 0 713 282 B1 reveals a canned motor for pumps with a can arranged between the rotor and the stator which separates the side carrying the forwarded medium from the electrical drive side, the stator having a sleeve-shaped base body which at least partly rests against the outside surface of the can to ensure that the construction is sufficiently stable even when the can has thin walls.
In the prior art, there are a large variety of construction methods for canned motors which can be realized as brush motors, asynchronous motors with rotary and AC operation or electrically commutated DC motors.
It is an object of the invention to provide a canned motor which can be realized as an electronically commutated DC motor and which has means to precisely measure the rotational position, rotational speed and/or rotational direction of the rotor to ensure that, on the basis of these measured variables, the motor starts up faultlessly in the correct direction and, moreover, to enable the rotational speed and number of revolutions of the motor to be precisely regulated down to very low revolutions.
This object has been solved by a canned motor comprising the features of claim 1.